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Diacylglycerol modulation of insulin receptor from cultured human mononuclear cells. Effects on binding and
Abstract:
Tumor-promoting phorbol esters alter binding of growth factors and hormones to their specific receptors. Action of diacylglycerols, endogenous phorbol ester analogues, on 125I-labeled insulin binding to its receptor from human cells was therefore investigated. A variety of 1,2-diacylglycerols and 1,3-diacylglycerols inhibited 125I-insulin binding to intact human monocyte-like (U-937) and lymphoblastoid (IM-9) cells in a dose-, time-, and temperature-dependent manner within 30 sec at 37 degrees C in a fashion analogous to that of the tumor-promoting phorbol diester 12-O-tetradecanoylphorbol-13-acetate (TPA). Inhibition of insulin binding by diacylglycerols, analyzed by Scatchard plot, seems to be due to altered binding affinity of the insulin receptor. Diacylglycerol effects were reversible, were seen regardless of the order of addition of 125I-insulin and diacylglycerols, and were demonstrated only with occupied insulin receptors. Corresponding fatty acids or phospholipids did not affect specific insulin binding to the intact U-937 cells. Diacylglycerols also inhibited binding of 125I-insulin-like growth factor (IGF) I but not that of 125I-human growth hormone (HGH) to the human cells. The non-tumor-promoting phorbols (phorbol, 4-alpha-phorbol, phorbol-12,13-distearate) did not affect insulin binding to intact cells. Both diacylglycerols and TPA stimulated internalization of 125I-insulin by U-937 and IM-9 cells. The ability of diacylglycerol to mimic the effects of TPA on the insulin receptor supports the concept of diacylglycerols as endogenous phorbol diester analogues even though the sole role of protein kinase C in our system is doubtful.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Diacylglycerols, like tumor-promoting phorbol esters, inhibit insulin binding to human cell receptors. This suggests diacylglycerols act as endogenous phorbol ester analogs, affecting insulin receptor affinity and stimulating insulin internalization.
Area of Science:
- Cell biology
- Biochemistry
- Endocrinology
Background:
- Tumor-promoting phorbol esters are known to modulate growth factor and hormone receptor interactions.
- Diacylglycerols are endogenous analogs of phorbol esters, suggesting a potential role in similar cellular processes.
Purpose of the Study:
- To investigate the effect of diacylglycerols on the binding of 125I-labeled insulin to its receptor in human cells.
- To compare the action of diacylglycerols with that of tumor-promoting phorbol esters on insulin receptor binding.
Main Methods:
- Utilized human monocyte-like (U-937) and lymphoblastoid (IM-9) cells.
- Assayed 125I-labeled insulin binding in the presence of various diacylglycerols and 12-O-tetradecanoylphorbol-13-acetate (TPA).
- Analyzed binding affinity using Scatchard plots and investigated effects on insulin internalization.
Main Results:
- Diacylglycerols inhibited 125I-insulin binding in a dose-, time-, and temperature-dependent manner.
- Inhibition was attributed to altered insulin receptor binding affinity, with effects being reversible.
- Diacylglycerols inhibited 125I-insulin-like growth factor I binding but not 125I-human growth hormone binding.
- Both diacylglycerols and TPA stimulated 125I-insulin internalization.
Conclusions:
- Diacylglycerols mimic the effects of TPA on the insulin receptor, supporting their role as endogenous phorbol ester analogs.
- The findings suggest diacylglycerols influence insulin receptor function and cellular uptake.
- The precise role of protein kinase C in these diacylglycerol-mediated effects remains uncertain.